Have you ever wondered, how a bean transforms from green to brown? Continue reading and you’ll learn the basics of roasting coffee.
If you ever saw a raw coffee bean (and we can’t imagine that you haven’t really), you can easily see how much a coffee bean needs to change to turn into that aromatic and beautiful brown piece of goodness that we adore. There are several phases of roasting coffee, each is important for the result – a beautifully roasted bean with a distinctive flavor and aroma.
Green coffee contains about 11% water, even if it has been dried in the sun. And this water is not something we want to keep in our roasted coffee, so the first phase of roasting coffee is drying the beans which happen somewhere up to 130 degrees Celsius. Why is this phrase important? If there is moisture inside the bean, the inside of a bean will be roasted less and could get an unpleasant, green vegetable- or grass-like taste.
The Maillard Reaction
From about 130 degrees Celsius upwards, the magic of roasting starts to happen. The beans turn yellow and then turn even darker, to the color of caramel or cinnamon. This is the phase that chemists could talk for hours about, as chemical processes inside the bean are now completely transforming the bean, especially the well known Maillard reaction that is responsible for the creation of flavors and aromas in coffee. The beans are also expanding quite a lot and eventually expand so much that you will hear …
… the first crack
The moment of glory for every coffee roaster! The bean has expanded, carbon dioxide and steam develop pressure inside it, and the bean bursts. You can hear when the first crack happens. This is the pivotal moment in coffee roasting because with the first crack the coffee becomes drinkable. Now it’s up to the roast master to decide how long the beans will be left in the roaster’s drum. Less time after the first crack generally enhances the core flavors of a coffee bean and leave a coffee roast that has more acidity and crisp flavors. Leaving the beans to roast longer will develop more sweetness and less clarity in a roast. Leave it too long and the coffee will taste bitter and ashy. This usually happens when you leave the beans to reach …
… second crack
At GOAT STORY, we are not fans of heavy roasts and when we roast our coffees, we avoid reaching second crack (except when we’re experimenting with roast times in the name of science, not flavor). The second crack is the second burst of a bean. The cracking sound is gentler than during the first crack and after the second crack, oils are squeezed out of a bean, leaving a slightly shiny surface. After the second crack the unique flavors, aromas, and acidity of coffee are mostly overwhelmed by roasted flavors and increased bitterness. But hey, some even like it that way.
No matter if the beans are roasted just past the first crack or up to the second crack or above when we decide to stop roasting them, it is time to cool them down as quickly as possible to stop the chemical reactions in them. Coffee roasters have a special cooling tray where coffee is tossed and turned, while a stream of cold air cools it from below.
During roasting, a lot of carbon dioxide is formed inside a bean. And when cooled down, this gas starts to exit the beans. That is why it is important to give the beans a few days to rest and push out the gas, as carbon dioxide prevents a good extraction of coffee. From our experience, the best time to use your freshly roasted beans is somewhat three to ten days after roasting for filter coffee and up to three weeks for espresso. And don’t forget to store the coffee properly, best in a coffee bag with a one-way valve that lets carbon dioxide escape, but doesn’t let oxygen creep into the bag.
We hope you enjoyed this little trip from green to brown!